The present invention relates to an apparatus (measurement inspection apparatus) for carrying out processing such as measurement, observation or inspection or the like of a sample (object) such as a semiconductor substrate, and a method (measurement inspection method) for carrying out measurement or inspection or the like using the apparatus, etc. The present invention relates particularly to a processing apparatus for imaging a sample and carrying out measurement, observation or inspection on a sample with the use of a scanning electron microscope (SEM), and relates to a method provided for the apparatus.
In a semiconductor manufacturing process, the miniaturization of circuit patterns formed on a semiconductor substrate (wafer) has been rapidly advanced. The importance of process monitoring to monitor such as whether those patterns are formed as designed is increasing more and more. For example, in order to detect the occurrence of abnormalities and failures (defects) in the semiconductor manufacturing process at an early stage or in advance, the measurement and inspection of the circuit patterns or the like on the wafer are carried out at the end of each manufacturing step.
Upon the above measurement/inspection, in a measurement inspection apparatus such as an electron microscope apparatus (SEM) using a scanning electron beam system, and a measurement inspection method corresponding thereto, an electron beam is applied to a target wafer (sample) while being scanned, and energy such as secondary electrons generated thereby is detected. Then, an image (measurement image or inspection image) is generated by signal processing/image processing or the like, based on the above detection, and the measurement, observation or inspection is carried out based on the image.
For example, in the case of a device (inspection device, inspection function) for carrying out the inspection of a defect in each circuit pattern, images of similar circuit patterns are compared with each other using the inspection image, and a point large in the difference therebetween is determined and/or detected as a defect. In the case of a device (measurement device, measurement function) for performing measurement on each circuit pattern, the amount of generation of secondary electrons or the like changes depending on the unevenness (surface shape) of a sample. It is therefore possible to acquire a change in the surface shape of the sample, etc. by evaluation processing of a signal of the secondary electrons. In particular, it is possible to measure the dimension values of the circuit pattern or the like by estimating the position of an edge in the image of the circuit pattern, particularly using that the signal of the secondary electrons is suddenly increased or decreased at the edge portion of the circuit pattern. Further, it is possible to evaluate the quality of processing of the circuit pattern, etc., based on the result of measurement thereof.
Further, in the case of a device (review device) for observing in detail, each defect detected by other inspection apparatus, a defect position is detected by a low-magnification secondary electron image, based on the position coordinates of the defect detected by other inspection apparatus. Then, an enlarged image of the defect is picked up by a high-magnification secondary electron image, and the defect is observed based on the enlarged image. Further, the feature amounts on the image of each defect are extracted from the enlarged image to perform defect classification.
In the measurement apparatus using the scanning electron beam system and the measurement method corresponding thereto, it is essential to move an observation point to each of several tens of inspection/measurement positions on the semiconductor wafer at high speed and improve throughput. A high-speed movable sample stage has therefore been developed, but its position accuracy is about several microns.
Mechanically controlling the sample stage in nanometer order is not practical in terms of the moving speed and production cost. To adjust the position of the sample stage with more accuracy, there has normally been adopted an image shift system for electrically moving the scan center coordinates of primary electrons. In this system, the sample stage is fixed. With an electron microscope, a relatively narrow visual field with high magnification is observed in a relatively wide visual field of a low magnification. The relatively narrow visual field is switched by shifting a scanning range of an electron beam.
Thus, in order to acquire the measurement image, the measurement apparatus using the scanning electron beam system needs to be equipped with a deflection scanning function capable of scanning an electron beam with respect to a measurement region lying in a target wafer (sample), and an image shift control function for moving the electron beam to the center of a range targeted for measurement.
There are two types of deflection system, electromagnetic deflection and electrostatic deflection, as a system for position movement and scan control of an electron beam. The electromagnetic deflection system applies a current signal to a coil installed in a column to generate a magnetic field and deflects and controls a passing electron beam by the Lorentz force. On the other hand, the electrostatic deflection system applies a required voltage signal to a multi-electrode electrode plate disposed in a columnar shape to generate an electric field and deflects and controls a passing electron beam by the Coulomb force. When comparing both systems, the electrostatic deflection system that is capacity-load driven has a scan speed that is ten times or more faster as compared with the electromagnetic deflection system that is inductor-load driven, and is used in a high-speed scan. On the other hand, since a mounting space is restricted and the sensitivity of a positional displacement due to electric noise is restricted in the electrostatic deflection system, it is not possible to increase deflection sensitivity (beam moving distance per unit voltage: um/V). Therefore, when the large-view beam movement and the deflection scanning are performed in the electrostatic deflection system, the required deflection voltage is increased.
An electron beam scanning system in a measurement inspection apparatus such as SEM according to a related art example and a method therefor will be described below. For example, a normal scan in a CD-SEM (critical dimension SEM) is called a TV scan or a raster scan or the like. Further, a scan having an n-fold increase in speed with respect to the TV scan is called an n-fold speed scan or the like.
A raster scan system or a TV scan system according to a related art example is accompanied by a problem that a difference occurs in the electrostatic charge quantity of a sample according to the shape or the like of each pattern formed on the sample. That is, a problem arises in that the accuracy of the observation, i.e., measurement or inspection of the surface condition of the sample is degraded, or it becomes impossible, like such as a reduction in image contrast or disappearance of the edge of each circuit pattern in an image obtained by detecting secondary electrons.
To cope with the above problem that the accuracy of the measurement/inspection is degraded, it is effective to shorten the irradiation time per unit region, i.e., decrease an irradiation charge density and reduce the electrostatic charge quantity of the sample or make it appropriate. To this end, raising the irradiation scanning speed of the electron beam like an n-fold speed or providing high-speed scanning is effective. Here, the electrostatic deflection system may be adopted to provide the electron beam deflection scanning function, thereby the high-speed scanning is provided.
Related art examples each related to the above measurement/inspection and electron beam control, there are known technologies described in JP-2006-093251-A (Patent Document 1), Republished Patent Publication No. WO01/033606 (Patent Document 2), JP-2001-283759-A (Patent Document 3), JP-1996-45460-A (Patent Document 4), JP-2012-249078-A (Patent Document 5), etc.
Patent Document 1 describes a technology or the like which measures pattern dimensions at a desired position on a cross sectional shape of each pattern. Patent Document 1 has described a dimension measuring method, comprising: acquiring a secondary electron image of a sample using a scanning electron microscope; creating an image profile of a pattern to measure its dimensions within the acquired secondary electron image using the secondary electron image; retrieving a model profile most matching with an image profile created out of a plurality of model profiles respectively corresponding to a plurality of patterns obtained from respective secondary electron images of a plurality of patterns already known in cross-sectional shape and dimensions stored in advance and different in shape; and determining the size of each pattern using information about the model profile obtained by retrieval. Patent Document 1 also describes an apparatus provided for the method.
Patent Documents 2 and 3 describes a method or the like as regards image shift control, in which even when the amount of movement by an image shift is large, the resolution and dimensional measurement accuracy are high.
Patent Document 4 describes that a response delay of a deflection position of an electron beam in an electron beam lithography apparatus is corrected accurately and at high speed.
Further, Patent Document 5 describes a driver integrated circuit which includes a differential input circuit, a level shift circuit and an output circuit divided. These circuits are arranged in three or more chips different in substrate potential so that an output voltage larger than a process breakdown voltage can be acquired.